Radiotelegraph system



Filed Jan. 13, 1931 m'l'n filter/z and as these afford facilities for only a restricted number'of connections," the messages Patented Feb. 28,; 1933 i I ?UNITED ST E JOHAN-GUNNARHOLMSTRbM, or srooxnormswnnnn i -BADITEIEGRAPHSSTEM I i Application filed January 13,1931, Serial No. 508,396,. and in Sweden";January14,1930. i

' The object of the present invention is a telegraph system affording possibilities for all telegraph oflices 'withinthe'same country or within any other-large area to intercommunicate in a direct way for'the transmission of messages by means of modern 'star't-anda stop teletype or facsimile telegraph appa-i' ratus. a 4 a v p i Under present'conditions the offices have to find their way along-the telegraphllines,

haveto besent through so -called collecting oflicesfor retransmission to their destinatlon.

. The'lines are not only expensive but'permit only'of a restricted number of possibilities of transmission and thus impose considerable delays upon the messages. 7 The present inventionhas adopted the use of radio communication for the connections between the several intercommunicating jofficess Each oflice isequipped with an'oscil latory receivingcircuit exactly tuned to a certain individual wave-length and with a either permanently tuned or capable of being tuned in a simple way to the wave-lengths of each of the other 'ofiices belonging to the same communication system. Inother'words, each office is provided either with as many circuits as there are corresponding offices or with a restricted number of circuits capable of be "ing adjustedyby thechange of their electric constants, to any of theci-rcuits of the corresponding offices. g I i Besides the necessary start-stop facsimile or other kind of telegraph apparatus suchas a Morkruni or other known teletype appa ratus, eachstation must therefore be provid-' ed with a switchingdevice including'a contact contrivan'ce for each of the oscillatory circuits. of the other officeswlthin the same communication area, these latter contrivances: being capable 'of being connected'by means of tl19 SWll3Cllll'lg device, to the transmitter and the "receiverof the sending ofiice. V In this way the telegraph apparatus is connected to the circuit emitting electromagnetic waves of a'frequ'ency corresponding to that of the office with which communication is required.

' large number of ofiicesor stations. great number of sendlng circuits, which are from the primary wave.

selectedby'means of a secondary wave high ,It being necessary, on accountof the great i 1 the characteristic frequencysent out by each,

office should "be'carefully tuned, be kept.con.-. stant and be exemptfrom strange frequencies produced by, attenuation orother disturbing causes. I 1 Y To attain this end it is proposedto utilize oscillatory circuits of very-small attenuation controlled in any known mannersuch as by ,the'p'iez'o-electric principle or by means of tuning forks;

In view of the large number of wavelengths required'it willbe advisable to choose the wavesa withi'n frequency bands that have .not yet been offi'c'ially appropriated'to any defined purposes With the aid of controlled oscillatory circuits having a constant fre-- quency it will be possible to reduce the separ'ation between two adj acent frequencies to a-very small amount and to occupy only a comparatively small frequency'b'and for a manner-{the difi'erent receiving stations all working on approximately thesame primary wave, andthe station required being determined by the deflection of the sending-wave The station is then or low frequency determined by the difference between the wave-lengths of the sending and the receiving ofiices. I As mentioned above the possibility of working many stations within a smallfrequency. band greatly depends upon the constancy ofthe individual frequencies used by the different stations. For this reason controlled oscillatory circuits areyunder present conditions best adapted to the purpose. ;It is also evident that the use of any contrivance intended to improve the coni stancy such as, thermostats and others may i also be desirable. l I In order to illustrate the invention a doe scription isgiven below of the operating proof the particular oscillatory circuit 7 of illus cedure applied in a telegraph system working on the lines in view. Reference is made in this description to the attached diagram.

The stations may be imagined to be designated by the letters A, 'B, C, D, E etc., N being the station shown on the diagram, while the other stations are practically duplicates thereof but are not shown. This latter station, as well as all the other stations, is,

preferably provided with astart-stop teletype apparatus, such as the Morkrum type, whose main construction forms no part of the invention, but whose impulse transmitter is designatedby '1 as'a key and the receiver thereof by 3 represents the aerial of the station, if any'such structure is used. The

aerial is supposed to 'includea grounded in-5 duction coil 4. To this latter coil are inductively coupled two coils, 15 and 6, and a feed back coil or tickler coil 40. Coil 5forms part trated station N, which includes A condenser 8 and 001i 5. By means of a swltching devlce conslstlng, forlnstance of a double conductor cord 9 andaplug10, coil 6 can be connected to any Of the 11A, llg llx, 114 111, 11 etc. arranged in a switchboard and corresponding to the respective other communiating stations (not shown). Each jack 11 graph system used.

is connected to its particularoscillatory circuit 12 12 12 ,12 12 12, ,12 and each of these circuits is tuned, by the adjustment of inductance 13 etc., and capacity 14 etc,

so as to correspond, together with coil 6, to each of the other imagined stations A, B, C. K, L, M, O'etc. By the insertion of plug'lO, for instance into jack 11 corresponding to station K the oscillatorycircuit 14 13 and 6 is connected to the aerial 3. r

The insertion of the plug further results in the connection of the; high tension points 30, 31, over the rest contacts 15 and 16 of relay 17, to the Valve receiver 41. If station p K is engaged this is revealed by the action of receiving device 2 upon the telegraph appa ratus. If ,nosuch action is visible station K is free and the telegraph apparatus of illustrated station N can be started. For this purq pose, contact 19 of the sender 1 is brought into direct contact with operating contact- 18, in

accordance with the requirements of the tele- For instance, when contact 19 touches contact 18, the circuit of a localbattery 20 is closed over relays 17 and 21. Relay 17 then connects the'high tension points 30, 31 of the circuit corresponding to station K to valve transmitter 22 producing the radiation from aerial 3 of waves corresponding to the characteristic frequency of "station K. Relay 21 is slow-working and therefore keeps contact 28 closed as long as the transmission lasts. Each time contact 19 is moved to rest contact 24 the current cir- A p cuit is closed through relay 25, thus effecting the connection of'valve'transmitter 22 to the particularoscillatory circuit 7 of the station over contacts 26 and 27. This will'result in the emission of the wave of illustrated sta vice, which starts the motor of its telegraph apparatus and depresses the key several times of the keyboard of station E. Electromagnetic waves of the frequency particular to present station N are then sent out and will work upon the circuit -7 of this station N.

i The valve receiver 41 of this station N is connected over rest contacts 28, 29 of relay 25, and the electromagnet 2 of-the receiver will therefore start the teletype apparatus or the like (not shown) and will work upon itsselooting and printing mechanism causing the letter E to be printed. This is the preferable calling procedure.

Station N replies to the call by inserting its plug 10 in' the E jackll of the calling 3 station and by pressing. down for instance the key of its start-stop'apparatus, of the station E thus indicating that the signal has been perceived and that the transmission may begin. When a key is pressed down at station N, the receiver 41 with the rceiving relay 2 isrcut out, by the action of relay 17, from the oscillatory circuit E of station N,

,while the transmitter 22 is switched in and produces'in this circuit oscillations of such intensity that the circuit acts as a transmitter and gives signals to station E of the nature determined bythe transmitting mechanism of the telegraph apparatus. This is possible because at station E the receiver-41 and the receiving relay2 are connected to the oscillatory circuit 7 corresponding to the wavelength of station E, when no key is depressed.

When the illustrated station'N is to send a messageto another station, K for instance. 5'

the cord plug 10 is inserted in jack 11;; of

the switchboard group of jacks shown. In 7 this way the transmitter 22 and the receiver 41 are connected to an oscillartory circuit tuned to the wavelength which is special to the station K. The sending operator at stationNnow starts the motor of the start-stop apparatus (not shown), either by pressing down a key (also not indicated on the diagram), by throwing over a switch or by some similar primary circuit closlng arrangement, andthen operates the key such as 1 of the keyboard several times. By this means oscillations are also produced in circuit 12 ,to whichthe apparatus has just been connected.

uess to receive.

gin transmission.

If the distant station K is free, it is apprised of the call throughthe fact that the motor of its apparatus is started and the letter N is printed on the apparatus. At. station K its plug is then inserted in its jack 11 and, by tapping on its key, announcesit's readi- WVhen the sending operator of present station N receives the signK'on her apparatus, she knows that she may be- She then sends her message'in the usual way and gets the receipt from distant station K,Whereupon cord plug 10 at this station N'is removed from jack 11 The receiving relays 2 of stations N and IQ being thus no longer subject to any impulses, a time-delay relay such as 21 breaks the circuits of the respective motors and makesthem stop. a I r I If at the moment when station N connects its apparatus to the oscillatory v circuitspecial to distant-station'K, the latter station is engaged in correspondence with some other station, this correspondence must not'be disturbed by station/N sending out oscillations characteristicto said station K.- Station' N must therefore'bemade aware of the fact that station K, is engaged. This can be arranged for in many ways and with notice taken of the fact that station K may be engaged either in receiving on its own wavelength or in sending on any other wave. One 1 solution of this problem consists in the transmitting oscillatory circuit 1%; of station N,

being used as a receiving circuit and made to work, in case impulses are receivedfrom the station K, upon the motor of the present station N, starting it, before the start key or switch of the same has been operated. The

sending operator of thisstation N will then,

have to wait some time after, insertingp'lug 10 in jack 11 say 15 or 30 seconds, before starting her motor. started after this time by impulses from the other distant station, she knows that station K is free and that she may start the motor and begin transmission from the oscillatory circuit 1%; of present station N. I

If station K isengaged in receiving waves of the frequency characteristic to stationK, the oscillatory circuit 12 of station N as soon as it has been connected to the N aerial of the station, receives the waves emitted and works on the receiving relay 2 of station N. a If said station K is engaged in sending on another'wavelengththan its own, special indicatory oscillations must be sent out from it during the Whole'time transmission is in progress. The present vinvention is equipped for this eventuality by making the oscillatory circuit 7 of imaginary station K emit oscillations of the Wavelength of this station, either continuously as long as transmission from said station K takes place. on another wavelength, or merely in the intervals between the signals transmittedbut during the If it has not been Whole, time transmission isgoing on from said station K in the manner desoribediabove inzrespect to presentstation N. The-latter alternative is presumably preferable, as it avoids simultaneous transmission from two circuits. a .e i a Evidently the contact devices of the switchingnequipment as well as. the leads to the equipment must be constructedso as to avoid influences upon the high frequency oscillatory circuits caused by 'changes'of capacity resulting fromthe switchboard operations; For this reason itis desirable that any actionexercised upon or originating from the oscil latory circuits should take place through in, termediary relays and that the currents working'upon, or closed or modified by,these relays should be either continuous or of low frequencyp i a .7 I a The present invention can bevused not only for start-stop butalso for facsimile telegraphs the samenotbeing shown as form,-

of oscillatory circuits havingidifiierent f'requencies lndividually corresponding with the reception. frequencies of all the stations in the group includingthat of the sending station, ,and'meansateach station including a switching device providing for the simultanee ous use at'said stationof two of said osci1 latory circuits for transmission purposes, one

forradiatingthe wave for traliic having av frequency corresponding with .the reception frequency of one of the other stations in the group, and of theother ofsaid two circuits for indicating that the, sending station is busy and having the same frequency as the IBCGP tion. frequency of said sending station.

I 2. Apparatus for intercommunication between a group of stations by means of radiant energy, including at each station, a

plurality of oscillatory circuits having --different frequencies individually correspond, ing with the reception frequencies of all the stations in the group including that, of the sending station, and means at each station including a switching device providing for thesi'multaneous use at said station of two of said oscillatory circuits for transmission purposes, one for radiating the wave for trafiic having affrequency corresponding with the reception frequency of one ofthe other stations in the group, and connected to reception devices in the sending station which .is automatically operable to receive incoming waves during idleness of the switching device and cessation of transmission from the station, and of the other of said two circuits for indicating that the sending station is busy and having the same frequency as the reception frequency of said sending station.

3. Apparatus for intercommunication between a group ofs'tations by'means of radiant energy, including at each station,-a pluality of oscillatory circuits having. difierent frequencies individually corresponding with the reception frequencies of all thestations in the group including that of the sending station, reception devices associated at each station with one of said oscillatory circuits,

and means at each stationincluding a switching device providing simultaneously for dissociation of said reception devices from said one oscillatory circuit and for the use at said station of two of said oscillatory circuits for transmission purposes, one for radiating the wave for trafiic having a frequency corresponding with the reception frequency of one of the other stations in the group, and of the other of said two circuits for indicating that the sending station is busy and having 09 the same frequency as the reception frequency of said sending station. i

4. Apparatus for intercommunication between a group of stations by means of radi ant energy, including at each station, a plurality of oscillatory circuits having different frequencies individually corresponding with the reception frequencies of all the stations in the group including that of the sendingstation, the oscillatory circuit at each station which corresponds in reception frequency to that of the wave transmitted thereby being self-oscillating during transmission of messages upon saidwave in order to distinguish onestation from the other in the grou'pby means of the dissimilarity of the beat oscillations whereby to provide for a large number of frequencies and corresponding stations within a relatively limited frequency band, and means at each station ineluding a switching device providing for the simultaneous use at said station of two of said oscillatory circuits for transmission purposes, one for radiating the wave for traific having a frequency corresponding with the reception frequency of one of the other stations in the group, and ofthe other of said two circuits for indicating that the sending station is busy and having the same frequency as the reception frequency of said sending station. 7

J OHAN GUNNAR HOLMSTROM. 

